Posted
by
Zonkon Wednesday April 02, 2008 @07:04PM
from the for-relative-terms-of-teeny-and-tiny dept.

AbsoluteXyro writes "According to a Space.com article, NASA scientists have discovered the smallest known black hole to date. The object is known as 'XTE J1650-500'. Weighing in at a scant 3.8 solar masses and measuring only 15 miles across, this finding sheds new light on the lower limit of black hole sizes and the critical threshold at which a star will become a black hole upon its death, rather than a neutron star. XTE J1650-500 beats out the previous record holder, GRO 1655-40, by about 2.5 solar masses."

There may already be microscopic (more like picoscopic) black holes all around us. The thing with black holes is they are only dangerous if you get close to them. If they are small they can whiz right through us without hitting anything, much like many other particles that pass through us all the time. I'm not saying that creating one would be a good idea, but if, on the off-chance, one were created by the LHC it will probably be innocuous. I wish I could make those sound less like famous last words.

There are going to be a near-infinite number of quantum-scale black holes and wormholes in whatever volume of space you care to imagine. They evaporate almost instantly. As for stellar black holes, the Chandrasaker Limit is 2.5 solar masses, with a relatively small margin of error. Absolutely nothing of interest will be learned until we're within 2.75 solar masses, because then we can define sensible confidence limits on what the value actually is.

As for stellar black holes, the Chandrasaker [sic] Limit is 2.5 solar masses, with a relatively small margin of error.

The value of the Chandrasekhar limit depends on how one performs the calculation, but typically it comes out to around 1.4 solar masses (not 2.5). But actually, this is not so much the interesting question, because the Chandrasekhar limit applies only to white dwarfs, whose mass is supported by electron degeneracy pressure [wikipedia.org]. This is only one type of a much broader concept called fermion degeneracy pressure.

For example, a neutron star is much denser than a white dwarf, and is supported by neutron degeneracy pressure instead of electron degeneracy pressure and hence the Chandrasekhar limit does not apply to neutron stars. The equivalent limit for neutron degenerate matter is called the Tolman-Oppenheimer-Volkoff limit [wikipedia.org]. Like the Chandrasekhar limit, this calculation is very dependent on the behavior of the degenerate matter, but UNlike the Chandrasekhar limit, we know very little about the properties of neutron degenerate matter, and so the uncertainty of the T-O-V limit is quite large; it is usually placed (as you can see in the wikipedia article that I link to) between 1.5 and 3.0 solar masses. And there are even denser objects that have been proposed (though not observed) made of quark degenerate matter, and the limit on the mass of these things is even more uncertain.

So the point is, there is still a good deal of physics that can come from the observation of a 3.8 solar mass black hole, as it can constrain various models of fermion degenerate matter.

I'm not saying that creating one would be a good idea, but if, on the off-chance, one were created by the LHC it will probably be innocuous. I wish I could make those sound less like famous last words.

What would be really scary is if the chief scientist says "Hold my beer and watch this" just before pushing the master ignition switch...

So what you're saying is that the odds of getting sucked into a black hole are proportional to its size. That sounds like something you could write a couple hundred to a couple thousand pages on and get a doctorate out of.

as long as Stephen Hawking is still alive, I am sure he can handle it. After all Stephen Hawking beat all the other great scientists in poker with Commander Data in the far future, so he should be smarter than Picard or Kirk. If anyone knows how to reverse a black hole it would be Hawking.

This newly discovered Black Hole is the final result of a Large Hadron Collider, that caused a microsopic black hole on the third planet formerly circling the former star now known as 'XTE J1650-500'. So, this is not a naturally occuring black hole, but an alien-created one. Sadly this alien species is now extinct so they can't tell us how to avoid their mistake.

Isn't it true that a black hole the size of a proton will evaporate (hawking radiation) at exactly the same rate as a proton decays?

No, it isn't. Protons are stable as best as anybody can tell -- if their life time is finite, then it is many orders of magnitude longer than the life time of the universe. While the Hawking-life time of a proton-mass black hole is miniscule (they evaporate faster, the less mass they have).

Not even close, do you really think that we could make a 3.8 solar mass black hole in the lab (that's several hundred thousand times the mass of our planet)? A more accurate term for the kind of black hole we might make in the lab is the hypothetical "microsingularity".

Fortunately those crazy atom smashing mad scientists don't have the power to do that. Someone hears the term mini-black hole and everyone freaks out. The artificial kind blinks out almost immediately. We just can't generate a sustainable singularity.

While it may be possible that this black hole was formed from a relatively small (to form a black hole) star, couldn't it also be the case that it just a really old black hole? Hawkings told of how black holes can 'evaporate' over time with lack of surrounding matter, perhaps that could be the case here.

Possible, but I believe they evaporate over the course of trillions of years via Hawking radiation. Based on recent evidence, the universe is only old enough for it to still have been the smallest yet discovered.

At least, if I were a scientist and not someone pulling this directly out of my ass, that might be what is happening here.

Possible, but I believe they evaporate over the course of trillions of years via Hawking radiation. Based on recent evidence, the universe is only old enough for it to still have been the smallest yet discovered.

It would be really interesting if we eventually found a class of black holes which could only predate the big bang.

It is true that black holes will evaporate over time, but they will also gain mass from infalling matter.

But!

The temperature of a black hole can be defined by the rate at which Hawking photons are streaming away from it. In the case of a black hole of a few solar masses, this temperature will be in the nano-Kelvin (I think -- don't hurt me if I'm wrong by a few orders of magnitude). Now remember everything in the Universe is sitting in a bath of cold photons from the Big Bang (i.e. the microwave background). These photons have a temperature of ~4 Kelvin.

So the CMBR at 2.7 Kelvin is about 165 million times warmer than this black hole.

Now as an academic aside, assuming the universe doesn't end in either a big rip or a big crunch, but rather a disappointing heat death, eventually the matter and energy in the universe would be so diffuse due to ordinary expansion that the temperature would drop below that 16.4 nano-Kelvin, and the hole would start losing mass. Over probably close to a goo

Since we're doing an academic exercise here, let's imagine the situation from the point of view of something falling into the black hole. If this something was looking backwards (i.e. out at the Universe, and not towards its impending doom), it would see all incoming photons strongly blue-shifted. To someone watching it fall into the black hole, they'd see it becoming more and more red-shifted, and slowing down more and more, until it appears to freeze, infinitely red-shifted, on the surface of the even

I take it you mean below, so any black hole above a certain size threshold won't decay until they eat all the background radiation in the universe. This size, presumeably, is above the lower limit for black hole creation in a supernova.

Yes, but the evaporation process is extremely slow. The following is an excerpt from the wiki article on Hawking Radiation [wikipedia.org]:

For a black hole of one solar mass (about 2 × 10^30 kg), we get an evaporation time of 10^67 years--much longer than the current age of the universe.

So even though this hole is evaporating like any other it could not have been much larger at the time of its formation (although it might have been somewhat smaller depending upon how much mass it has sucked in during its existence so far), even if it had existed since the beginning of the Universe which is impossible because stars, and especially lower mass stars like the one that mos

No, the time it takes for a stellar black hole to evaporate is much, much longer [wikipedia.org] than the age of the universe, even assuming that no matter is falling into it. For a mass this large, the time is on the order of 10^69 years. It is only microscopic black holes that decay quickly. For instance, if we take a proton-proton collision at the LHC, where each proton has an energy of 7 TeV, and form a black hole out of it, it would have a mass of 10^-23 kilograms and would evaporate in 10^-84 seconds, which is the

You're close to the correct reasoning. What has actually happened here is that the black hole in question has simply had wave after wave of matter thrown at it until it hit it's preset kill limit.Once that occurs, the black hole shuts down and it's simply a matter of time until it evaporates into nothing.

I believe the final thing that appeared to enter the hole and allow it to reach it's kill limit was a space cruise ship, Tita-something or other. Closely followed by an upper-class-looking golden robot. I t

Perhaps you can answer a question for me. If I understand the concept correctly (and stop me where I go wrong), the event horizon can be defined as the point where any light that were to be ejected (I know, I know not possible) from the singularity perpendicular to the tangent (straight "up") would stop and return.

This is the Newtonian description of a black hole. The relativistic description is considerably more complicated. First of all, you must always start any relativistic description by stating your reference frame - i.e. who is making the observations? The Schwarzschild metric (which is the standard non-rotating black hole) takes the observer to be someone infinitely far away and not moving relative to the black hole.
According to that observer, there is a singularity at the event horizon. Anything inside th

They can't figure out the "critical threshold" because there isn't one. It all depends on too many variables to set a universal limit (hehehe get it...universal:-P) It depends on how much nuclear activity there is still going on when it start collapsing and what the amount of heavier atoms is and the amount of other things orbiting the star and any other forces affecting the star at that time and how fast it's moving and spinning. Mass is a smaller part of the calculation than they're making it sound like. If they're going to factor everything in just to find some minimum mass, well duh, two particles and a hell of a lot of force. Haven't they suggested that in that big particle accelerator aka donut of doom. So yeah, a critical mass threshold doesn't exist.

I believe according to the link you sent that the Chandrasekhar limit is the upper limit for how massive a non-rotating star can be before it collapses into a black hole (there are obviously plenty of stars with more mass than this but they have rotation or other things that prevent them from collapsing). What the article is talking about is a theoretical lower limit for how small something can be before naturally forming into a black hole. This is not necessarily the same since you could have a smaller bod

I've studied Astronomy. The Chandrasekhar limit is a classic piece of Astrophysics that should be part of any popular article discussing the limiting size of an object becoming a black hole. I don't know of a mechanism that might cause a smaller body to form a black hole. That force would need to be applied in such a way as to overcome electron degeneracy pressure.1.4 solar masses is much smaller than the masses we're observing for black holes. My point was we haven't approached this yet. There are other fo

The article you've pointed to states that this limit was initially estimated at 0.7 solar masses (lower than the Chandrasekhar limit) but that modern estimates are between 1.5 and 3 solar masses (which is higher), so yes sure this is definitely relevant. However the classic discussion centers around the more easily computed Chandrasekhar limit. In other words BOTH limits apply, it's just that we don't know which is lower. I haven't looked at this stuff for about 5 years. When I did we focused on the Chandra

Shaposhnikov and his colleague Lev Titarchuk of George Mason University used this method to "weigh" XTE J1650-500 and found a mass of 3.8 suns. This value is well below the previous record holder GRO 1655-40, which tips the scales at about 6.3 suns.

Call me when they make that black hole using that collider they talk about in a different comment.

While black holes is not my area, I can tell you that when someone talks about the size of the black hole, they refer to the event horizon, since you can't really measure anything going on inside it.The mass of the black hole is the most defining characteristic.

Sure you can measure what's going on past the event horizon of a black hole. All you have to do is make your camera's velocity exceed the force created (or rather possessed) by a photon going at the speed of light, and presto! You now have a camera that can probe farther into the gravimetric field of a black hole than light by itself.

I thought that Black Holes had no dimensions, but this one is several miles across. Where have I gone wrong?

A black hole, conventionally, consists of an event horizon surrounding a region of space from which you can't send information to the external world. This region of space is not a point, it has a well-defined circumference. (Because of the non-euclidean nature of general relativity, it doesn't actually have a well-defined radius (since you can't measure across the middle!) but people usually just consider the radius as if it were defined as the circumference divided by 2 pi, and don't worry about the fact that you can't actually measure it.)

At the center of the black hole is, according to general relativity, a point singularity, which indeed has no dimensions.

Actually, that's only true of a non-rotating (or Kerr) singularity. All natural black holes will be rotating (the black hole maintains the rotational momentum of the pre-collapse mass). In a rotating black hole, the singularity is actually a ring (or torus). Inside that ring/torus, there is a tear in space.

It was this tear that lead, if I recall, to the original conjectures of a white hole, and the Einstein-Rosen bridge.

Yeah, I thought about mentioning that, and decided what I was writing was getting a bit complicated already

All natural black holes will be rotating (the black hole maintains the rotational momentum of the pre-collapse mass).

Well, maybe. Actually, rotating black holes radiate away angular momentum, and they also preferentially eat material that reduces their angular momentum, so it's an open question as to whether real black holes will be rotating. Probably, because the accretion disk is likely to be rotating, and it swallows up the accretion disk and gains the momentum from it, but I'm not sure you can necessarily say that all natural black holes will rotate.

In a rotating black hole, the singularity is actually a ring (or torus). Inside that ring/torus, there is a tear in space.
It was this tear that lead, if I recall, to the original conjectures of a white hole, and the Einstein-Rosen bridge.

Actually, the Einstein-Rosen bridge comes from the maximum analytical extension of the Flamm embedding, way predating the Kerr solution. (It's a very trivial embedding, z = sqrt(r). The extension is z = plus or minus sqrt(r).) Turns out that the extended Flamm embedding is misleading, and a Schwartzschild black hole isn't a wormhole after all. But that wasn't obvious.

Actually, the Schwarzchild solution does have a well-defined radius. In fact, the problem is that it has many well-defined radii, depending on what you mean by the term (as you point out, this comes about because of the non-Euclidean nature of the geometry). The commonly quoted "Schwarzschild radius" r = 2GM/c^2 is obtained by taking the area of the horizon and figuring out which "r" you would have to plug into A = 4 pi r^2 [true for a flat space sphere] to get the right result. Taking the circumference an

No, actually it doesn't. What is usually called the Schwartzschild "radius" is not actually a radius by the definition of the word, "distance to the center".

In fact, the problem is that it has many well-defined radii, depending on what you mean by the term (as you point out, this comes about because of the non-Euclidean nature of the geometry). The commonly quoted "Schwarzschild radius" r = 2GM/c^2 is obtained by taking the area of the horizon and figuring out which "r" you would have to plug into A = 4 pi r^2 [true for a flat space sphere] to get the right result.

Exactly. You can calculate the area (which is well defined) and divide it by 4 pi, and you are free to call that the radius if you like. Or, equivalently, divide the circumference by two pi. But you can't measure the distance to the center.

Taking the circumference and dividing by 2 pi would achieve the same result. However, it is quite possible to figure out the proper distance between the horizon and the singularity by measuring the distance an infalling observer would travel. This distance is finite.

Finite... and timelike. It would be a little like trying to define the radius of a circle if you're standing on the circumference, and the center is next Tuesday at noon.

A problem can occur if you try and use constant time slices, using the "natural" time coordinate as defined by an observer far from the black hole. This gives silly results, but that is only because of badly behaved coordinates.

Within the event horizon, any choice of coordinates is rather badly behaved, because there is no well-behaved stationary coordinate system.

it doesn't actually have a well-defined radius (since you can't measure across the middle!)

Why do you need to measure *across* the middle to measure the radius?

Is there a (theoretical) problem with using some kind of high tech space calipers to measure the radius without going anywhere near the 'middle'?

You could, but the result wouldn't really be right. A black hole is like that blessed +2 bag of holding that has much more room inside it than the space that it actually encompasses. I never really studied general relativity, but I think that when an object is in a strong gravity field, it becomes shorter (or everything else becomes longer). This means that the notion of length gets a bit weird. Similarly, if you used calipers to measure the diameter of a block hole, the sides of the calipers would no long

If you are standing apart from the event, some light year(s) away, you can calculate the distance between objects by simple trigonometry. But if you are standing inside the event horizon... If there is no dimensions how can one measure distances?:)

From the objects' points of view, they don't know when they cross the event horizon.

From an observer's point of view, the objects never reach the event horizon. They just appear to move slower and slower.

Black hole's really do mess up any concept of Euclidean distance. The best way of picturing it, is that it is a hole in space-time; for all intents and purposes, the space inside the event horizon simply doesn't exist.

In theory, they radiate themselves out of existence over time through Hawking Radiation [wikipedia.org]. They constantly release energy, which reduces their mass. If they lose more mass than they swallow, then their event horizon will shrink. Eventually, there'll be no mass left, and no black hole.

What you've described is a way that energy can be created from nowhere. If what you suggest were right, we'd all be doomed, as any small black hole would get bigger through Hawking radiation, and would then consume everything.

Wouldn't the volume be technically infinite? Or at least undefined? It has a measurable surface area (if you're talking about the event horizon), but the curvature of space would make the radius, hence the volume, infinite.

And just following that through... wouldn't that make the average density of a black hole zero? Mass/volume with infinite volume...

"If they were able to make a small blackhole, and it got "loose" and fell to the center of the Earth, the pressures at the Earths core would force material into it so fast that even a very small one would gobble us up very fast. I am not sure what the exact pressure is at the Earths core but it could force material through even a very small "hole" very quickly. I do agree that once it gobbled up the Earth, it would just continue to orbit the Sun, and the Moon would still orbit the blackhole as if it were the Earth..."

No, you should read this thread.

First of all, a black hole that falls to the center of the earth, wouldn't stop there, but would continue falling up on the other side, just to plunge in again, and on and on, because there's no "friction" on the black hole.

Second, there have been posted in this thread a lot of calculations of the speed at which it would gobble up matter.Don't forget that the black hole we're talking about here IS MUCH MUCH SMALLER THAN A PROTON. As such, pressures on *atomic* level (such as in the center of the earth) matter little: the black hole travels most of the time in the empty space between nucleae.A way to calculate the probability of hitting a nucleus (and somehow imagining that it would gobble up the entire nucleus, which is MUCH MUCH bigger than the black hole itself - which is a worst-case scenario) is done by calculating the "cross section" of the black hole and its probability to cross a nucleus on its voyages through the earth. We know its speed (just falling), and knowing the cross section and the density of nucleae, we can estimate how many nucleae it could eat per unit of time.

for a MUCH LARGER black hole, about the size of a proton, weighting a billion tons (figure that! A black hole *the size of a proton* weights a billion tonnes ; we're talking here about black holes that weight 10 TeV or 10^(-24) kg - go figure how small it is !)

For more exotic calculations which are more severe, orion made some, and arrived at a time to eat the earth ~ 10^46 years.

All this in the following rather un-natural hypotheses:- no Hawking radiation (which would make the black hole evaporate almost immediately)- production of black hole EXACTLY IN THE CENTER OF GRAVITY of the collision (no remnant particles)- very high production rate, producing billions of black holes per second.

I am not a physicist, but from what little physics I have had, and from reading threw the thread/flamewar, I dont think we have to worry about the LHC

And you know this how exactly? I guess you might be talking about a micro black hole, maybe orders of magnitude smaller than an electron. In that case I would have to agree that the earth would seem to be mostly empty space, like a whole galaxy to a human sized spaceship. But if it is anything much larger than that I would imagine that there would at least be some frictional forces as it plummeted through the dense metallic core of the earth like a lead brick through air. If its mass were great enough I wo

Absolutely zero. The smaller a black hole is, the faster it radiates away its mass in the form of energy. A microscopic black hole would cease to exist in a very small amount of time. One created in a particle accelerator would cease to exist almost instantly, leaving only energy behind. It would be possible to detect evidence of its presence by the energy signature it left, but that's about it. If such black holes can even be created in a particle accelerator, then they will have been created by gamma